Cathode ray signal reproducing tube



Nov. 1942- P. T. FA-RNSWORTH CATHODE RAY SIGNAL REPRODUCING TUBE Filed Oct. 9, 1940 INVENTOR PHI 0 I. FARNSWORTH Patented Nov. 10, 1942 UNITED STATES PATENT OFFICE CATHODE RAY SIGNAL REPRODUCING TUBE I Philo '1. Farnsworth, Brownfield, Maine, asslgnor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application October 9, 1940, Serial No. 360,459

2 Claims.

.ning the same with a beam of electrons modulated in accordance with received television signals. Incase the reproduced image is to be projectedin an enlarged scale, an intense luminescent image is required. Since the time allotted to each picture element is extremely small, a very intense electron scanning beam is required. Such a beam is ordinarily detrimental to the life of the screen material. Moreover, it is highly desirable to provide a storage effect in connection with the scanning beam, that is, to extend the period of excitation of the luminescent screen by the beam for each scansion to an interval, which is longer than that allotted to the scanning of a single picture element, in order to obtain a gain in luminosity of the reproduced image while preventing flicker.

It is an object of the present invention, therefore, to provide a new and improved cathoderay signal-reproducing tube having a longer life and utilizing a storage efiect.

In accordance with the present invention, television pictures are reproduced by first developing a beam of electrons and then successively developing, in response to said beam, electron images corresponding to parts of a complete optical image to be reproduced. The successivelydeveloped electron images are focused to successive positions at a plane, whereupon they are converted into light to reproduce the complete optical image. In a preferred embodiment of the invention, the successive electron images correspond to successive lines of the picture to be reproduced,-;and they are developed by thermionic electron emission in response to an electron beam which is modulated in accordance with the television signal. The conversion of the electron images into light also preferably is accomplished by means having a delay or storage effect, such as, for example, an incandescent screen. I

A storage effect is thus provided by both the thermionically electron-emissive elements and the incandescent picture-producing screen, which continue their electron and light emission, respectively, beyond the actual scansion intervals or periods of excitation. Preferably, the total period of thermionic emission, in response to each excitation by. the electron beam, is approximately that of a line-scanning period, thereby greatly increasing the brilliance of the image developed on the screen while substantially reducing flicker of images successively developed thereon.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawing. and its scope will be pointed out in the .appended claims.

In the accompanying drawing: Fig. 1 is a schematic diagram, partly in section,

of a picture-reproducing tube embodying the present invention connected in circuit for operation; and

Fig. 2 shows an enlarged perspective view of the thermionically electron-emissive elements scanned by the modulated beam of electrons.

Referring now more particularly to Fig. 1, there is shown a television picture-reproducing tube comprising an evacuated envelope I having a main cylindrical portion 2 and a neck portion 3 connected at one end thereof.

For the purpose of developing an electron beam, there is provided at the end of the tube neck 3 an electron gun I of conventional construction comprising an indirectly heated cathode 5, a control electrode 6 and an anode I. At the end of the main envelope portion 2, there is provided an optical window 8 and adjacent thereto, preferably intersecting the axis of the neck portion 3, there is provided a supporting member 9 secured to a lead-in wire l0 and carrying a plurality of thermionically electron-emissive elements II in line formation. This line has a length equal to that of a scanning line. The elements ll preferably comprise short lengths of tungsten wire and are arranged to be impacted by the electron beam developed in the electron .gun 4. The number 01' thermionically electronemissive elements I I is at least equal to the number of picture elements per scanning line and preferably greater.

For the purpose of developing a luminous image, there is positioned at the end of the main envelope portion 2, opposite the optical window 8, a luminescent screen It adapted to be impacted by electrons emitted by the thermionically electron-emissive elements comprising a back plate l3 and a multitude of incandescent particles l4, preferably in the form of a pile of short lengths of tungsten wire. A supporting lead 15 is provided for the screen [2, as shown. For modulating the electron beam developed by the electron gun 4, there is provided a pair of television signal input terminals 1 l6, l6 coupled to the control electrode 6 of the electron gun by means of a condenser l1 and a grid-leak resistor 18. For focusing the electron beam upon the thermionically electron-emissive elements ll, there is provided a focusing coil 20 connected in series with a voltage source or battery 2| and a rheostat 22.

For the purpose of deflecting the electron l l and preferably beam along the line of thermionically electronemissive elements II, there is provided a pair of scanning coils 23, 23 disposed about the neck 3,

as shown, and connected to a source of deflect-..

ing current; 24, which may be of conventional design.

A focusing coil 25 is disposed around the main envelope 2 between the electron-emissive elements II and the incandescent screen I2, and is connected to a voltage source or battery 26 and a rheostat 21. The coil 25 focuses the emission from the elements II upon the screen I2. For the purpose of defiectirg the electrons emitted by the elements II across the screen l2, there is provided a pair of deflecting plates 28 and 29, disposed within the envelope portion 2 and preferably of curved shape, as shown. The plates 28 and 29 are connected by way of supporting leads 30 and 3|, respectively, to a source of deflecting voltage 32, which may be of conventional design.

For providing operating voltages for the tube, there is provided a battery or voltage source 33 connected between the anode I of the electron gun and the thermionically electron-emissive elements I I, and a second battery or voltage source 34 connected between the elements II and the incandescent elements I4, as shown. A third battery 35 is connected between the anode I and the cathode 5, which may be grounded, as shown.

An optical lens system schematically indicated by the lens 35 is positioned adjacent the window 8 outside the envelope I for projecting the luminous image developed on the screen I2 upon a projection screen 31.

Fig. 2 shows an enlarged perspective view of the supporting means 9 and the thermionically electron-emissive elements II attached thereto.

In the operation of the system, an electron beam is developed by the electron gun 4 and modulated in accordance with picture signals applied to the input terminals I6, I6. The mod ulated electron beam is focused upon the thermionically electron-emissive elements II by means of the focusing coil 20, and scanned thereacross by means of the magnetic fields developed by the deflecting coils 23, 23. The power of the modulated electron beam is of such magnitude that the individual thermionically electron-emissive elements II become heated, upon the impact of the electron beam, to temperatures at which thermionic electron emission takes place. The temperatures to which the elements I I are raised naturally correspond to the intensity of the electron beam, and hence the thermionic electron emission from these elements is in accordance with the picture signal applied to the input terminals I6, I6. The elements II are preferably 50 designed that their temperature remains above the minimum temperature for electron emission for a period substantially equal to that of a linescanning interval so that, upon return of the electron scanning beam, the temperature of the element has dropped just below the point of emission. Due to the fact that the thermionic electron emission continues for a very substantial time beyond the extremely short time of primary electron impact on each of the elements II, a very appreciable storage effect is obtained, corresponding in duration to a scanning line.

An electron image due to the emission from the elements II is focused upon the incandescent elements I4 of the screen I2 by means of the focusing coil 25, and is deflected thereacross from top to bottom by means of the deflecting plates 28 and 29, energized by the source of deflecting voltage 32. Upon impact of the electrons emitted by the members II, the temperatures of the incandescent elements I4 are raised to points at which these elements are incandescent and radiate light in accordance with the intensity of the electron emission impacting them, and hence in accordance with the picture signal applied to the input terminals I6, I6.

Elements I4 of the screen I2 are preferably so designed that their temperatures, after being raised to points of incandescence, decay during a picture-frame interval to a value slightly below that required for incandescence. Hence, due to the fact that the interval of incandescence may extend beyond the time allotted to the scanning of a single picture element up to the entire duration of a picture frame, a second storage effect is realized. The over-all storage eifect which may be utilized with the present arrangement, therefore, corresponds substantially to a frame interval.

The luminous image developed by the incandescent elements I4 is projected by means of the projection lens 35 upon the projection screen 31.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A cathode-ray signal-reproducing tube comprising an electron gun for developing a beam of electrons, means for modulating said beam in accordance with a signal to be reproduced, a plurality of separate linearly disposed and conductively connected thermionically electron-emissive elements adapted to be heated to emission temperatures by said modulated electron beam for successively developing electron images each corresponding to a single line of the complete optical image represented by said signal, a target responsive to electron impact for converting electron energy into light energy, and means for focusing said successively developed electron line images upon said target at such positions as to reproduce said complete optical'image.

2. A cathode ray signal reproducing tube comprising an envelope having a main portion and a neck portion extending therefrom at an angle, an electron gun in said neck portion for developing a beam of electrons, means for modulating said beam in accordance with a signal to be reproduced, a plurality of separate linearly disposed and conductively connected thermionically electron emissive elements disposed in said main portion of said envelope and adapted to be heated to emission temperatures by said modulated beam for successively developin electron images each corresponding to a, single line of the complete optical image represented by said signal, a target in said main portion of said envelope responsive to electron impact for converting electron energy into light energy, said target being disposed in the path of electrons from said electron emissive elements and out of the path of electrons from said gun, and means for focusing said successively developed electron line images upon said target at such positions as to reproduce said complete optical image.

PHILO 'I. FARNSWORTH. 

